1. Field of Invention
The present invention relates to fluid control test plugs. In particular, the present invention relates to locally actuated, fail safe (i.e. normally closed), fluid material control test plugs adapted for use inside of fluid material transmission conduits.
2. Description of the Prior Art
The present invention is particularly adapted for use inside of substantially straight conduits of uniform cross-section, (as well as within tapered conduits), wherein it may be desirable to seal at least one end of the conduit, (for example, to pressure-test the conduit or to prevent unwanted flow through the conduit).
Valves which control fluid material flow through conduits are well known. In most prior devices, it is necessary to build the valve into the conduit itself--as, for example, with common gate valves. The problem of such valves is they become, more or less, permanent fixtures in the conduit, thus affecting fluid flow even when the valve is not in use (i.e. when the valve is open). Furthermore, such valves also have a disadvantage in that they have the inherent characteristic of not being easily re-positionable within, or removable from, the conduit.
It is well known in the prior art to use expandible-type test plugs, in pipe lines in order to determine whether the installation will withstand the operating pressure necessary for proper functioning of the pipeline. Many such prior test plugs are of the type having a resilient plug that is expanded into sealing engagement with the inner wall of the conduit to be tested in order to compartmentalize the conduit.
After such prior test plugs are in place, a pressurized fluid is typically injected into the conduit up to a predetermined pressure to determine if the installation will withstand operating conditions. A great disadvantage with such prior devices is that they are normally open. Should, for any reason, there be a loss of pressure to the plug, such as, for example, due to a leak in an air supply line, then the valve would automatically open, allowing an undesired flow of fluid material therethrough.
Remotely actuated prior pneumatic valves are known which are normally closed, such as the device illustrated in U.S. Pat. No. 3,022,977. Prior devices of this type generally comprise a resilient elastomeric vessel which, under normal conditions, is of sufficient cross-sectional area to occupy, and therefore seal off, the cross-sectional area of a conduit within which it is disposed. When, by use of a remote vacuum source, air pressure is exhausted from the elastomeric vessel to below atmospheric pressure, the volume of the vessel decreases and its cross-sectional area also decreases, thereby breaking the seal between the outer wall of the elastomeric vessel and the inner wall of the conduit. A problem of such prior devices is that they require a remote vacuum source for their operation.
A similar group of prior devices is represented by the pneumatic valve illustrated in U.S. Pat. No. 4,185,806. Prior devices of this type typically comprise a resilient elastomeric vessel which, under normal conditions, is of cross-sectional area sufficient to occupy, and therefore seal off, the cross-sectional area of a conduit within which it is disposed. When, by use of a remote source, presesurized air is forced into the elastomeric vessel, the volume of the vessel expands and its cross-sectional area (as measured perpendicular to the conduit's wall) decreases, thereby breaking the seal between the outer wall of the elastomeric vessel and the inner wall of the conduit.
One problem of prior devices of this type is that they depend on the volumetric expansion of their elastomeric vessel in order to open such valves.
A great disadvantage of devices of this type is inherent in their reliance on the volumetric expansion of the elastomeric vessel in order to open the valve. Because the volume of such elastomeric vessels must vary substantially during operation of the device, such prior vessels must be made almost entirely of elastomeric, (i.e. readily deformable), material. Consequently, such prior devices are inherently incapable of withstanding large axial loads--as such loads deform the elastomer and compromise the integrity of the seal--and are, therefore, only adapted for use in low pressure applications (such as described in U.S. Pat. No. 3,022,977), or when used inside of tapered conduits or in conjunction with rigid accessory restraining supports, (each of which as described in U.S. Pat. No. 4,185,806).
Still another problem of prior devices of this character that they rely upon a remote source of pressurized fluid for their operation.
Another problem of such prior devices is that, if the elastomeric vessel should, for any reason, develop a leak, the vessel will automatically depressurize, thereby making it extremely difficult, if not virtually impossible, to remove the damaged plug from inside of the conduit.